In recent years, flat panel displays are utilized in various products and fields. The flat panel displays are expected to have a further increased size, a further enhanced image quality, and further reduced electric power consumption.
In this situation, organic EL display devices, which include an organic EL element which utilizes electroluminescence (hereinafter referred to as “EL”) of an organic material, have been attracting much attention as all-solid-state flat panel displays having excellent properties in terms of low voltage driving, fast response characteristic, self-light emission property, wide viewing angle characteristic, and the like.
An organic EL display device has a configuration in which, for example, an organic EL element is provided on a substrate, which is constituted by a glass substrate or the like and is provided with a TFT (thin-film transistor), and the organic EL element is electrically connected with the TFT.
For example, a full-color organic EL display device is in general arranged such that organic EL elements including luminescent layers of respective colors red (R), green (G), blue (B) are provided in array on a substrate as subpixels, and a color image is displayed by using TFTs so as to selectively cause the organic EL elements to emit light with desired luminances.
As such, in order to manufacture an organic EL display device, luminescent layers made from organic light-emitting materials, which emit light of respective different colors, need to be formed, in a predetermined pattern, for respective organic EL elements.
As a method for forming such luminescent layers in a predetermined pattern, for example, vacuum deposition, inkjet printing, the laser transfer method, and the like have been known. For example, in a low molecular organic EL display device (OLED), vacuum deposition is used in many cases.
In vacuum deposition, a mask (also called shadow mask) having an opening of a predetermined pattern is used, and a substrate, with which the mask is in close contact and to which the mask is fixed, is arranged so that a vapor-deposited surface of the substrate faces a vapor deposition source.
Then, deposition particles (a material for film formation) supplied from the vapor deposition source are deposited on the vapor-deposited surface through the opening of the mask, so that a thin film having the predetermined pattern is formed. The deposition is carried out with respect to each color of the luminescent layers, and this is called “selective vapor deposition”.
Patent Literatures 1 and 2 each describe a method of carrying out selective vapor depositions of luminescent layers of respective colors by gradually moving a mask with respect to a substrate.
In such a conventional selective vapor deposition method, a mask that is equal in size to a substrate is used. When the deposition is carried out, the mask is fixed to the substrate so as to cover a vapor-deposited surface of the substrate.
It is therefore necessary in the conventional selective vapor deposition method to enlarge the mask as the substrate is made larger.
However, in a case where the mask is enlarged, a gap between the substrate and the mask is more easily formed by self-weight bending and extension the mask. Moreover, a size of the gap varies depending on a position of the gap on the vapor-deposited surface of the substrate.
This creates a problem that high-precision patterning is not easily carried out by the conventional selective vapor deposition method, so that displacements of a vapor deposition position and color mixture occur.
Further, in the conventional selective vapor deposition method, enlarging the mask results in causing a frame or the like for holding the mask to become enormous and have an increased weight as well. This may result in more difficult handling and deteriorated productivity and safety.
Moreover, in the conventional selective vapor deposition method, a vapor deposition device and a device accompanying the vapor deposition device are also made enormous and complicated. This results in difficulty in designing the devices and an increased installation cost.
As described above, it is difficult by the conventional selective vapor deposition method to form a high-resolution patterned vapor-deposited film on a large substrate. Currently, on a large substrate for which a mask of, for example, 60 in. or larger is used, the selective vapor deposition has not been successfully carried out on a large scale for mass production.